Preheat oven to 425°F and line a jumbo muffin tin with liners.
Whisk together flour, baking powder, baking soda, and salt.
In another bowl, whisk melted butter, oil, and sugar.
Add eggs and egg yolk, then stir in buttermilk and vanilla.
Combine wet and dry ingredients until just mixed.
Toss chocolate chips with flour and gently fold into batter.
Let batter rest for 15–20 minutes.
Fill muffin liners almost to the top.
Mix crumb topping ingredients until crumbly and sprinkle over muffins if using.
Bake at 425°F for 5–7 minutes.
Reduce oven temperature to 350°F and continue baking for 18–22 minutes.
Cool slightly before serving.